This article reviews some requirements for licence-plate readers (LPRs), then describes the high-definition digital cameras and LPRs developed by Computer Recognition Systems (CRS). A reader must have high recognition performance on licence plates from all countries, at maximum vehicle speeds. It must have extensive communications facilities and image and text database capabilities, ability to handle supplementary colour images, and various other features. 100% recognition is not possible, for various reasons. A good LPR has a long-term recognition rate of 85% to 95% for unobstructed licence plates, averaged over all weather conditions and times of day, and 97% in favourable circumstances. CRS has increasingly been using high-definition digital cameras, using over 625 lines, during recent years. Although such cameras are more expensive and more complex to use, they are likely to be used in the future for all but the least demanding applications. Whatever camera is used should be sited to give an unobscured view of the licence plate, as square-on as possible. CRS's LPR, the NRS, has been developed continuously during the last 20 years. Its applications include security, surveillance, tolling violation enforcement, parking and access control, speed violation detection, and dynamic lorry weight distribution measurement.
Samenvatting